1. Field of the Invention
This invention is directed to an improved suspension system for the polymerization of p-methylstyrene. It is more particularly concerned with a novel extender for suspension polymerization of p-methylstyrene.
2. Description of the Prior Art
As is well known to those familiar with the art, bead-shaped polymeric materials are generally produced in suspension polymerization. In such polymerization, vinyl monomers are suspended or dispersed in an aqueous medium in the presence of a suspension stabilizer and a polymerization initiator. The suspension stabilizer acts to prevent undesirable agglomeration of the polymerizing monomer and produce high molecular weight polymer in bead form. Instable dispersions result in agglomeration of the polymeric material into large masses.
Well known suspensions stabilizers that are widely used are the difficultly soluble phosphates, such as calcium, strontium, and magnesium phosphates. While under certain conditions these difficultly soluble phosphates serve to stabilize suspensions, they are erratic in behaviour. Various materials have been proposed that function as an auxiliary or "extender" for the difficultly soluble phosphate to increase its effectiveness as a suspension stabilizer. The anionic surface active agents must be used in carefully controlled amounts to avoid adverse effects. In addition, the range of utilizable concentrations is very narrow, making it difficult to follow the commercial practice of varying the polymer bead size by varying the amount of anionic surface active agent. Another proposed type of extender is a soluble salt of alkyl phosphoric acid.
Insofar as is now known, the extenders used in suspension system of this invention, i.e., sulfonated poly(p-methylstyrene), have not been proposed. Surprisingly, the suspension system of this invention appears to be specific for polymerization of p-methylstyrene. Attempts to use it in suspension polymerization of styrene resulted in collapse of the suspension.